netdev - Re: [PATCH v3 01/11] xen/manage: keep track of the on-going suspend mode

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Date:   Sun, 13 Sep 2020 13:07:36 -0400
From:   boris.ostrovsky@...cle.com
To:     Anchal Agarwal <anchalag@...zon.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        jgross@...e.com, linux-pm@...r.kernel.org, linux-mm@...ck.org,
        kamatam@...zon.com, sstabellini@...nel.org, konrad.wilk@...cle.com,
        roger.pau@...rix.com, axboe@...nel.dk, davem@...emloft.net,
        rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
        peterz@...radead.org, eduval@...zon.com, sblbir@...zon.com,
        xen-devel@...ts.xenproject.org, vkuznets@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        dwmw@...zon.co.uk, benh@...nel.crashing.org
Subject: Re: [PATCH v3 01/11] xen/manage: keep track of the on-going suspend
 mode


On 8/21/20 6:25 PM, Anchal Agarwal wrote:
> From: Munehisa Kamata <kamatam@...zon.com>  
>
> Guest hibernation is different from xen suspend/resume/live migration.
> Xen save/restore does not use pm_ops as is needed by guest hibernation.
> Hibernation in guest follows ACPI path and is guest inititated , the
> hibernation image is saved within guest as compared to later modes
> which are xen toolstack assisted and image creation/storage is in
> control of hypervisor/host machine.
> To differentiate between Xen suspend and PM hibernation, keep track
> of the on-going suspend mode by mainly using a new API to keep track of
> SHUTDOWN_SUSPEND state.
> Introduce a simple function that keeps track of on-going suspend mode
> so that PM hibernation code can behave differently according to the
> current suspend mode.
> Since Xen suspend doesn't have corresponding PM event, its main logic
> is modfied to acquire pm_mutex.
>
> Though, accquirng pm_mutex is still right thing to do, we may
> see deadlock if PM hibernation is interrupted by Xen suspend.
> PM hibernation depends on xenwatch thread to process xenbus state
> transactions, but the thread will sleep to wait pm_mutex which is
> already held by PM hibernation context in the scenario. Xen shutdown
> code may need some changes to avoid the issue.
>
> [Anchal Agarwal: Changelog]:
>  RFC v1->v2: Code refactoring
>  v1->v2:     Remove unused functions for PM SUSPEND/PM hibernation
>  v2->v3:     Added logic to use existing pm_notifier to detect for ARM
> 	     and abort hibernation for ARM guests. Also removed different
> 	     suspend_modes and simplified the code with using existing state
> 	     variables for tracking Xen suspend. The notifier won't get
> 	     registered for pvh dom0 either.
>
> Signed-off-by: Anchal Agarwal <anchalag@...zon.com>
> Signed-off-by: Munehisa Kamata <kamatam@...zon.com>


BTW, just to make sure --- Thomas' comments about commit message format
(SoB order, no changelog, etc) apply to all patches, not just #5.


-boris